Generally, a loading arm is a device which is used to transfer liquid freight, including crude oil and liquefied natural gas (LNG), from a transport vessel to storage equipment which is installed on land. The loading arm is a kind of coupling device for coupling the transport vessel to a quay wall, and has a coupling structure having articulations to compensate for variation in the depth of water when the vessel is moored and freight is transshipped. Further, several loading arms are simultaneously coupled to the side of a vessel to load and unload the vessel.
Meanwhile, when LNG is loaded or unloaded, an additional gas loading arm is connected to be parallel to the LNG loading arm, thus helping carry boil-off gas.
The transshipment and transfer of liquid freight between objects floating at sea are performed as follows. That is, a fender is inserted between the floating objects, and the floating objects are coupled to each other using a hose, thus transferring fluid between the floating objects. However, when waves rise, the floating objects may be damaged due to a collision therebetween, and thus may cause a fire. Therefore, actually, it is difficult to transfer liquid freight between the floating objects.
In order to solve the problem, the following method of transferring crude oil was devised. That is, floating objects, such as vessels, are arranged at regular intervals in a longitudinal direction, and are connected to each other using rope. Subsequently, in order to prevent collisions between the floating objects, a suitable amount of driving force is applied in opposite directions. In such a state, hoses couple bows to sterns. Such a method is used to transship freight between Floating Production, Storage and Offloading (FPSO) installations and transport vessels.
However, the method is problematic in that, when more than one hose is used, the hoses may become tangled. Further, the hose usually sags and soaks in seawater, so that low-temperature liquefied gas, such as cryogenic LNG, is vaporized in the transfer hose by seawater, which has a high specific heat, and thus the low-temperature liquefied gas cannot be used. Meanwhile, when one desires to transfer LNG, boil-off gas must be simultaneously returned. Thus, the above-mentioned method is not suitable for an LNG transfer operation, which requires two hoses.